In the past, there has been a supercharger that rotates a turbine at a high speed by exhaust gas of an internal combustion engine of a vehicle or the like and supercharges an internal combustion engine by driving a compressor sharing a rotating shaft with the turbine. Since the drive of such a supercharger requires the exhaust gas of the internal combustion engine, such a supercharger cannot cope with the supercharging of an internal combustion engine at the time of start, rapid acceleration, or the like. Accordingly, an electric supercharging device, which drives a rotating shaft of the compressor by an electric motor, is used. An example of this electric supercharging device is disclosed in PTL 1. The electric supercharging device disclosed in PTL 1 will be described below with reference to FIG. 6.
As shown in FIG. 6, an electric supercharging device 102, which is assembled with an air supply flow passage 101 of an engine 100 that is an internal combustion engine, includes a compressor 104 that is provided so as to face the air supply flow passage 101, an electric motor 106 that drives the compressor 104, a controller 108 that controls the electric motor 106, a steering lever that is manually operated by a driver, supercharging amount adjusting means 110 for commanding the controller 108 to control the amount of supercharging of the electric supercharging device 102, display means 112 that is formed of a display provided on an instrument panel (not shown) disposed in front of a driver's seat and displays the amount of supercharging, and a power source 114 such as an in-vehicle battery or an alternator.
The controller 108 includes a drive unit 116 that drives the electric motor 106 and a control command unit 118 that controls the drive unit 116 according to the amount of supercharging set by a driver. For example, an inverter is built in the controller 108, and the controller 108 converts electric power, which is supplied from the power source 114, into alternating current by the inverter and controls the rotation speed of the electric motor 106 by arbitrarily changing a voltage and a frequency.
Since the voltage of an electrical storage device such as a battery, which forms the power source 114, is low (for example, 12 V), it is necessary to allow large current flow in the electric motor 106 to rotate the electric motor 106 at a high speed. When a large amount of current is allowed to flow in the electric motor 106, the amount of heat generated from the electric motor 106 is increased. For this reason, a cooler for cooling the electric motor 106 needs to be added.